(19)
(11) EP 0 394 010 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
22.04.1992 Bulletin 1992/17

(43) Date of publication A2:
24.10.1990 Bulletin 1990/43

(21) Application number: 90304139.0

(22) Date of filing: 18.04.1990
(51) International Patent Classification (IPC)5: H05B 6/68
(84) Designated Contracting States:
DE FR GB IT SE

(30) Priority: 19.04.1989 JP 99407/89
09.05.1989 JP 115330/89

(71) Applicant: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Kadoma-shi, Osaka-fu, 571 (JP)

(72) Inventors:
  • Yamaguchi, Kimiaki
    Nara-shi (JP)
  • Kasai, Isao
    Nabari-shi (JP)
  • Sakai, Shinichi
    Yamatokoriyama-shi (JP)
  • Murakami, Susumu
    Shiki-gun, Nara-ken (JP)
  • Akiyoshi, Mitsuo
    Nara-shi (JP)
  • Otsuka, Akinori
    Haibaracho, Uda-gun, Nara-ken (JP)
  • Sano, Masaaki
    Yamatokoriyama-shi (JP)

(74) Representative: Smith, Norman Ian et al
F.J. CLEVELAND & COMPANY 40-43 Chancery Lane
London WC2A 1JQ
London WC2A 1JQ (GB)


(56) References cited: : 
   
       


    (54) Heating apparatus


    (57) A heating apparatus such as a microwave oven in which thermal energy of high-temperature vapor generated by heating an object (2) is detected by a pyroelectric element (5) and a resulting detection signal is used to control (stop) a heat source (3) such as a microwave source, etc. Among AC voltages generated by the pyroelectric element due to heat exchange of the pyroelectric element, a voltage of a polarity generated at the time of heat discharge (temperature decrease) of the pyroelectric element (5) is selectively eliminated through a circuit means (41). A voltage generated by heat exchange between air moving slowly in a heating chamber (1) and the pyroelectric element caused by the rotation of a turntable (33) or the like is eliminated by another circuit means (43). A control section (4) controls the operation of the heat source by deciding an output signal of the pyroelectric element by comparing it with a detection level determined in accordance with a noise level for a predetermined length of time after the start of the heating operation. Erroneous detection is thus prevented which otherwise might be caused by a noise voltage generated in the pyroeelctric element by the thermal energy of a hot air staying in the heating chamber after the energization of the heat source (3) or a second heat source (34, 35).







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